Many types of organic liquids, such as various forms of petroleum, oil, “sour” gas, fuel, organic solvents and other hydrocarbons, as well as waste water, mine tailings, oils, coal and effluents of various processes contain sulfur (S). The presence of sulfur in these liquids has been correlated with damage to both the natural environment as well as to man-made environments. For example, sulfur in petroleum has led to the corrosion of pipelines, pumping and refinery equipment, and premature breakdown of combustion engines. In addition, combustion of sulfur-containing liquids results in sulfur dioxide pollution of the atmosphere, thereby contributing significantly to extended occurrences in acid rain. Acid rain has lasting deleterious effects on aquatic and forest ecosystems, as well as agricultural areas located downwind of combustion facilities. To combat these problems, several methods for desulfurizing fuels and coal have been developed.
When sulfur is predominantly present in its organic forms, it can be removed chemically by hydro-desulfurization processes, which involve reacting natural gas, hydrocarbon-based fuels and other such products with hydrogen gas at elevated temperatures in the presence of selected catalysts. These methods have many technical shortcomings and are quite expensive. As a result, many practitioners of this art have turned their attention to microbial desulfurization processes (MDS) as potentially viable alternative options; that is, the use of microbial metabolic processes to desulfurize liquids.
Several microorganisms have metabolic pathways involving sulfur. The metabolic pathways of bacteria such as those exemplified by Thiobacillus sp., Sulfolobus sp., Hansenula sp., and Cryptococcus albidus, have been used for removing sulfur from coal and/or coal slurries. Rhodococcus sp. and their enzyme derivatives, in combination with hydro-desulfurization methods, have also been used to remove organic sulfur from hydrocarbon fuels. Other microorganisms exemplified by Rhodococcus rhodochrous, Bacillus sphaericus, Pseudomonas sp., Campylobacter sp., Leptospirillum ferrooxidans, Thiobacillus ferrooxidans and a variety of mixed cultures have also been used for removing sulfur from various liquids.
Sulfur and sulfur-containing compounds removed from organic liquids, waste water, mine tailings, oils, coal and effluents of various processes can be used in numerous industrial applications. For example, sulfur and/or sulfur-containing compounds can be used to manufacture cellophane and rayon, can be used as a component of fertilizers, can be used in pharmaceuticals, dyestuffs and agrochemicals, can be used as a fungicide or pesticide and can be used in fermenting wine.